1. Field of the Invention
The present invention relates to a piezoelectric thin film element and a piezoelectric thin film device. In particular, it relates to a piezoelectric thin film element and a piezoelectric thin film device using a piezoelectric material that contain no lead, such as a lithium potassium sodium niobate, or the like.
2. Description of the Related Art
Piezoelectric substances are processed into various piezoelectric elements according to various purposes, and are utilized widely as functional electronic components, such as an actuator, which applies voltage to cause deformation, a sensor, which conversely uses deformation of the piezoelectric element to generate voltage, or the like.
In recent years, from environmental concerns, the development of piezoelectric substances that contain no lead has been desired. For example, a lithium potassium sodium niobate (general formula: (NaxKyLiz)NbO3 (0<x<1, 0<y<1, 0<z<1, x+y+z=1), etc. has been developed. The lithium potassium sodium niobate possesses as good a piezoelectric property as Pb(Zr1−XTiX)O3 based perovskite type ferroelectrics (PZT), and is therefore expected as a major candidate for a lead-free piezoelectric material. The lead-free piezoelectric thin film may be used to produce a head for a high-definition high-speed inkjet printer, a low-cost micro gyrosensor, which are small in environmental load, and the like.
Also, with reduction in size and enhancement in performance of electronic components of each kind, there is a strong demand for size reduction and performance enhancement of piezoelectric elements as well. However, when the thickness of a piezoelectric material produced by a conventional piezoelectric element production method using sintering is particularly below 10 μm that approaches the size of crystal grains constituting the piezoelectric material, the effect thereof becomes non-negligible. This causes noticeable property variation and degradation of the piezoelectric material. In order to avoid the property variation and degradation of the piezoelectric material, piezoelectric thin film production methods have been studied that apply thin film technology, etc. replaced for the sintering method.
As a conventional lead-free piezoelectric thin film element, a piezoelectric thin film element using a dielectric film formed of an alkali niobium oxide based perovskite compound is known (refer to Patent Document 1). The piezoelectric thin film element disclosed by Patent Document 1 comprises a substrate formed of MgO, etc., a lower electrode formed on the substrate, a buffer layer formed of BaTiO3, etc., and formed on the lower electrode, an alkali niobium oxide based perovskite compound represented by the general formula (NaxKyLiz)NbO3 (0<x<1, 0<y<1, x+y+z=1), a piezoelectric thin film formed on the buffer layer, and an upper electrode formed on the piezoelectric thin film, in which the piezoelectric thin film is formed by RF magnetron sputtering, CVD, PLD, coating, or the like.
Since the piezoelectric thin film element disclosed by Patent Document 1 has the structure as described above, it has a good piezoelectric property.
Patent Document: JP-A-2007-19302.